After walking across a large, treeless hill called the Field of Fire, over a drawbridge and beneath a Spanish coat of arms, you step into nearly five hundred years of history. In 1539, King Charles I of Spain ordered the construction of a defense for Puerto Rico de San Juan Bautista. The initial fort was small and ill-equipped. In 1587, his son, Philip II of Spain, commissioned Battista Antonelli to design an elaborate expansion. Antonelli was the chief architect of Spanish forts throughout the New World. The citadel was named Castillo San Felipe del Morro in honor of the king. In English, it means the Castle of Saint Philip on the Headland. Additional enhancements were made under King Felipe IV in the mid-17th century and King Charles III one hundred years later. By the late 1780s, El Morro was called a Defense of the First Order and was one of the best fortifications in the Americas. It proved worthy of these accolades several times. El Morro was attacked by the buccaneer Sir Frances Drake in 1595, by George Clifford, 3rd Earl of Cumberland, three years later, the Dutch in 1625, the British in 1797 and the American Navy in 1898. In 1915, the first shot by the United States in World War I was fired from El Morro on a German ship. It was also a U.S. military post during WWII. After the U.S. Army moved out in 1961, El Morro was turned over to the U.S. National Park Service.